The long term goal of the proposal is to explain the neuronal bases of simple forms of behavior at the level of signal processing in all of the elements of the functional neuronal network. Toward this goal, we would first try to achieve simultaneous recording of the action potentials and subthreshold signals in both cell bodies and processes in a restricted number of neurons using preparations in which simultaneous recording of action potentials from most neuronal cell bodies (but not processes)is already possible. This study would be based on experiments using multi-site optical recording techniques. Optical recording of subthreshold potential changes from small neuronal processes is still exceedingly difficult because of the small signal size relative to noise. At present it can only be used under most favorable and thus very limited experimental conditions. The improvement in sensitivity that we hope to obtain will be based on two approaches. First we would exploit the idea of limiting the application of impermeant voltage-sensitive dyes to a restricted number of neurons in the network and not stain the whole structure. This may be accomplished by intracellular application of dyes into cell bodies. Intracellular staining would improve spatial resolution of optical recording as well as signal-to-noise ratio. Second, we propose to continue the search for new dyes that would give better optical signals after either extra- or intracellular application. We propose to test analogs of most successful dyes from different categories of voltage sensitive compounds and to use several different invertebrate preparations that are especially suitable for optical recording studies of neuronal correlates of behavior. With the best dye/preparation combination we then propose to develop the recording and analysis of signal integration at the level of neuronal processes of individual cells within a functional network. The knowledge we obtain about how normal behavior is generated in these primitive animals will help us understand mental disorders such as depression, drug addiction or schizophrenia.